In portable electric tools such as portable drills, screwdriver/drills and screwdrivers, it is desirable to reverse the direction of rotation of the motor to facilitate, for example, the loosening and removal of screws, the removal of a drill bit from a hole or the removal of a thread cutting tool out of a bore after cutting a thread in the bore by reverse rotation of the cutting tool.
One conventional method for reversing universal motors is to reverse the electrical connection of the brushes and stator windings. To obtain optimum performance and maximum brush life in a reversing motor, there must be a compensation mechanism for the distortion in the magnetic field, called "neutral plane shift" that results from the interaction of the rotor and stator fluxes. One such mechanism is the shifting of the brush location about the armature axis in the direction that is opposite of the direction of rotation of the armature. Such shifting avoids sparking and excessive brush and commutator wear. In addition, the sparking will cause electrical noise to be transmitted into the power source supplying the electrical energy for the tool.
One such brush shifting and reversing switch assembly is disclosed in U.S. Pat. No. 4,748,353 in which the brush shifting and reversing switch mechanisms are combined into a single assembly. The manual actuator for the mechanism is located on the rear of the motor housing in the plane of the brushes. Such a location has been found to be undesirable for two reasons. First, the location of the manual actuator in this position increases the bulkiness of the motor housing which is undesirable in many portable power tools. Secondly, it has been found that users prefer the actuator to be located just forward of the power (trigger) switch.